Electrical balance duplexer

Abstract

An electrical balance duplexer (EBD) is provided in an example comprising a first transformer comprising a first at least part of a transformer winding and a second at least part of a transformer winding and a second transformer comprising a third at least part of a transformer winding and a fourth at least part of a transformer winding, wherein the first at least part of a transformer winding is connected in series with the third at least part of a transformer winding. The EBD also comprises a first amplifier having an output connected to the first at least part of a transformer winding and / or the third at least part of a transformer winding, and a second amplifier having an input connected to a node between the second at least part of a transformer winding and the fourth at least part of a transformer winding. The second at least part of a transformer winding is connected in series with the fourth at least part of a transformer winding between a first antenna node and a second antenna node, wherein the first antenna node is for connection to a first antenna and the second antenna node is for connection to a second antenna.

Description

[0001] ELECTRICAL BALANCE DUPLEXER

[0002] Technical Field

[0003] Examples of this disclosure relate to an electrical balance duplexer (EBD), for example in a transceiver or a wireless communications device.

[0004] In band full duplex (IBFD) solutions, where transmission and reception occur simultaneously on the same frequency channel, suffers from self-interference (SI) due to the strong transmit signal being present at the antenna while receiving the weak receive signal. Successful IBFD relies on Sl-cancelation in multiple steps. These include antenna transmitter and receiver isolation, radio frequency (RF) and analog front-end (AFE) cancellation, and cancellation in the digital back end (DBE).

[0005] There are four well known transmitter and receiver isolation techniques. These are: 1) separation of transmit (Tx) and receive (Rx) antennas, 2) use of circulators, 3) use electrical balanced duplexers (EBDs), and 4) separation of Tx and Rx polarizations. All four methods have drawbacks as explained below.

[0006] Transmitter and receiver isolation (also referred to herein as Tx-Rx isolation) is the first step in Sl-cancellation, and reduces the level of the transmitter signal at the receiver input. It is needed to reduce linearity requirements of a low noise amplifier (LNA) in the receiver, and to avoid compression of the LNA and other parts in the receive chain before next level of Sl- cancellation. Furthermore, Tx-Rx isolation also relieves requirements on succeeding cancellation in RF, AFE, and DBE.

[0007] Obtaining good isolation by separation of Tx and Rx antennas is highly unattractive due to the increase of the physical dimensions of the device on which the antennas are mounted.

[0008] External circulators are typically large and bulky, and require a non-reciprocal path that uses a magnetic material and therefore cannot be integrated on chip. Recent advances have demonstrated integrated circulators using non-reciprocal n-path filters, they however constitute a difficult design task and are highly limited in power handling capabilities, bandwidth, and isolation. Furthermore, to obtain high Tx-Rx isolation with a circulator the antenna impedance must be well matched. Separation of TX and RX polarization for two collocated antennas provides limited isolation and limits the transceiver to use one polarization in each direction, limiting achievable link capacity. Another problem is that polarization alignment is needed between two units communicating, and misalignments will cause signal losses.

[0009] EBDs are easy to integrate, especially for high frequency transmissions, give excellent isolation between transmitter and receiver circuitry, but require an accurately tuned dummy load that tracks the antenna impedance to achieve good isolation. They also have a fundamental 3 dB insertion loss (IL) for both transmit and receive signals, to which circuit parasitics will add further loss. Katanbaf et al, “Two-Way Traffic Ahead,” IEEE Microwave Magazine, February 2019, pp. 22-35, discloses an overview of methods for Tx selfinterference cancellation toward full duplex integrated radios.

[0010] Figure 1 is a circuit diagram of an example of an EBD 100. The EBD 100 includes a balanced power amplifier (PA) 102. A first winding 104 of a first transformer 106 and a first winding 108 of a second transformer 110 are connected in series between the outputs of the PA 102. A node 112 between the first windings 104 and 108 is connected to ground.

[0011] A second winding 114 of the first transformer 106, a second winding 116 of the second transformer 110 and a matching impedance 118 are connected between an antenna (represented by impedance 120 connected to ground) and ground. The impedance 118 is a tuned dummy-load matched to the antenna impedance (Rantenna) 120. A node 122 between the second windings 114 and 116 is connected to the input of a LNA 124.

[0012] Summary

[0013] Some examples of this disclosure may mitigate one or more of the above-identified problems. For example, examples of this disclosure may avoid the 3dB fundamental insertion losses while achieving good isolation between transmit and receive signals.

[0014] One aspect of the present disclosure provides an electrical balance duplexer (EBD). The EBD comprises a first transformer comprising a first at least part of a transformer winding and a second at least part of a transformer winding, and a second transformer comprising a third at least part of a transformer winding and a fourth at least part of a transformer winding, wherein the first at least part of a transformer winding is connected in series with the third at least part of a transformer winding. The EBD also comprises a first amplifier having an output connected to the first at least part of a transformer winding and / or the third at least part of a transformer winding, and a second amplifier having an input connected to a node between the second at least part of a transformer winding and the fourth at least part of a transformer winding. The second at least part of a transformer winding is connected in series with the fourth at least part of a transformer winding between a first antenna node and a second antenna node, wherein the first antenna node is for connection to a first antenna and the second antenna node is for connection to a second antenna.

[0015] Another aspect of the present disclosure provides an electrical balance duplexer (EBD). The EBD comprises a first transformer comprising a first at least part of a transformer winding and a second at least part of a transformer winding, and a second transformer comprising a third at least part of a transformer winding and a fourth at least part of a transformer winding, wherein the first at least part of a transformer winding is connected in series with the third at least part of a transformer winding. The EBD also comprises a first amplifier having an output connected to a node between the second at least part of a transformer winding and the fourth at least part of a transformer winding, and a second amplifier having an input connected to the first at least part of a transformer winding and / or the third at least part of a transformer winding. The second at least part of a transformer winding is connected in series with the fourth at least part of a transformer winding between a first antenna node and a second antenna node, wherein the first antenna node is for connection to a first antenna and the second antenna node is for connection to a second antenna.

[0016] Another aspect of the present disclosure provides a device comprising the electrical balance duplexer (EBD) of either of any of the above aspects.

[0017] Brief Description of the Drawings

[0018] For a better understanding of the embodiments of the present disclosure, and to show how it may be put into effect, reference will now be made, by way of example only, to the accompanying figures, in which:

[0019] Figure 1 is a circuit diagram of an example of an EBD;

[0020] Figure 2 is a circuit diagram of an example of an EBD according to embodiments of this disclosure;

[0021] Figure 3 illustrates an example of a device with antennas mounted on surfaces on opposite sides of the device; Figure 4 is a circuit diagram of another example of an EBD according to embodiments of this disclosure; and

[0022] Figure 5 is a circuit diagram of another example of an EBD according to embodiments of this disclosure.

[0023] Detailed Description

[0024] The following sets forth specific details, such as particular embodiments or examples for purposes of explanation and not limitation. It will be appreciated by one skilled in the art that other examples may be employed apart from these specific details. In some instances, detailed descriptions of well-known methods, nodes, interfaces, circuits, and devices are omitted so as not obscure the description with unnecessary detail. Those skilled in the art will appreciate that the functions described may be implemented in one or more nodes using hardware circuitry (e.g. analog and / or discrete logic gates interconnected to perform a specialized function, Application Specific Integrated Circuits (ASICs), Programmable Logic Arrays (PLAs), etc.) and / or using software programs and data in conjunction with one or more digital microprocessors or general purpose computers. Nodes that communicate using the air interface also have suitable radio communications circuitry. Moreover, where appropriate parts of the technology can additionally be considered to be embodied entirely within any form of computer-readable memory, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein.

[0025] Examples of this disclosure provide an electrical balance duplexer (EBD) and devices, such as communication devices, that include the EBD. Instead of having a tuned dummy-load matched to the antenna impedance, a second antenna, electrically isolated from the first antenna, is connected. The two antennas may in some examples be oriented to radiate in different directions with limited overlap, such as being located on different or opposite sides of a device. The two antennas can have either the same or different polarization. This effectively avoids the fundamental 3 dB insertion loss of prior art EBD arrangements as no power is dissipated in a dummy load, either for Tx or Rx signals.

[0026] However, in some examples where the two antennas radiate in different directions, half the transmit power will be transmitted in one direction and half in the other direction. In Rx mode, for example, half the power will be received from one direction and half from the other direction. As for a prior art EBD, the Rx and Tx signals are in differential mode and common mode, respectively, at the two antennas. If the antennas were omni-directional their combined radiation patterns would be very different in Rx and Tx, but having different directions of the antenna patterns with small overlap between them, the combined radiation patterns will be similar in Rx and Tx. This may be desirable for example for communication with a single device (e.g. base station, access point, relay, wireless communication device, radio unit, User Equipment (UE), etc) in both Rx and Tx. Furthermore, in non-line-of-sight conditions, signals via objects in different directions may in some examples be combined.

[0027] Compared to applying the Tx and Rx directly at one antenna each, separated by polarization, examples of this disclosure can achieve an improved Tx -Rx isolation. Examples of this disclosure can also use both polarizations for higher communication capacity, e.g. using one EBD per polarization, and thus not needing polarization alignment between devices. Examples of this disclosure may be particularly advantageous for devices or scenarios where a compact solution and short latency achieved by full duplex would be important advantages, such as repeaters or virtual reality (VR) headsets for example. In the case of VR headsets, for example, one antenna can be placed on one side of the headset and the other antenna can be placed on the other side of the headset.

[0028] Figure 2 is a circuit diagram of an example of an electrical balance duplexer (EBD) 200 according to embodiments of this disclosure. The EBD may be included in some examples in a device such as a wireless communications device. The EBD 200 includes a first transformer 202 comprising a first at least part of a transformer winding 204 and a second at least part of a transformer winding 206, and a second transformer 208 comprising a third at least part of a transformer winding 210 and a fourth at least part of a transformer winding 212.

[0029] The first at least part of a transformer winding 204 is connected in series with the third at least part of a transformer winding 210. In some examples, the first transformer 202 and second transformer 208 may be a single transformer, or the first at least part of a transformer winding 204 and the third at least part of a transformer winding 210 may be a single transformer winding (e.g. two halves of a single winding).

[0030] The EBD 200 includes a first amplifier 214 having an output connected to the first at least part of a transformer winding 204 and / or the third at least part of a transformer winding 210. For example, in the example shown, the first amplifier 214 is a balanced power amplifier (PA) whereby the series connected first at least part of a transformer winding 204 and third at least part of a transformer winding 210 are connected between the balanced outputs of the PA 214. In some examples, a node 216 between the first at least part of a transformer winding 204 and the third at least part of a transformer winding 210 is connected to a reference voltage (which in examples of this disclosure may be ground or a positive supply voltage). In examples where the first at least part of a transformer winding 204 and the third at least part of a transformer winding 210 are parts of the same winding, the node 216 may be a centre tap for example.

[0031] In other examples, the first amplifier 214 may have a single unbalanced output, in which case the output may be connected for example to the node 216. In such examples, the first at least part of a transformer winding 204 and the third at least part of a transformer winding 210 may be connected in series between the same node, e.g. a reference voltage or ground. The first transformer 202 may then have a reversed coupling polarity compared to the second transformer 208. Alternatively, for example, the first at least part of a transformer winding 204 and the third at least part of a transformer winding 210 may be connected in series between the PA output and reference voltage or ground. In either of these examples, the ground connection to node 216 may be omitted.

[0032] The EBD 200 also includes a second amplifier 218 having an input connected to a node 220 between the second at least part of a transformer winding and the fourth at least part of a transformer winding. In the example shown in Figure 2, the second amplifier is a low noise amplifier (LNA). The second at least part of a transformer winding 206 is connected in series with the fourth at least part of a transformer winding 212 between a first antenna node 222 and a second antenna node 224, wherein the first antenna node is for connection to a first antenna and the second antenna node is for connection to a second antenna. In the example shown in Figure 2, the first antenna node 222 is connected to a first antenna (represented by impedance 226 connected to ground) and the second antenna node 224 is connected to a second antenna (represented by impedance 228 connected to ground). In some examples, the first antenna 226 and the second antenna 228 have a matched impedance.

[0033] In some examples, the second at least part of a transformer winding 206 and the fourth at least part of a transformer winding 212 may be a single transformer winding (e.g. two halves of a single winding). For example, the first transformer 202 and second transformer 208 may be a single transformer, in which case the node 220 may be a centre tap.

[0034] In some examples, a coverage pattern (also referred to herein as a radiation pattern) of the first antenna 226 is different to a coverage pattern of the second antenna 228. For example, the coverage pattern of the first antenna 226 partially overlaps with the coverage pattern of the second antenna 228, or does not overlap with the coverage pattern of the second antenna 228. As a result, in some examples, a signal received at a device including the EBD 200 is not cancelled out or is only partially cancelled out at the node 220. In some examples, the first antenna 226 and the second antenna 228 are mounted on different surfaces of a device, or on surfaces on opposite sides of the device. Figure 3 illustrates an example of a device 300, such as a wireless communication device, in which antennas are mounted on surfaces on opposite sides of the device 300. Specifically, a first antenna 302 (which may for example correspond to first antenna 226) is mounted on a first surface 304 of the device 300, whereas a second antenna 306 (which may for example correspond to second antenna 228) is mounted on a second surface 308 of the device 300, where the second surface 308 is on an opposite side of the device 300 to the first surface 304.1

[0035] In some examples, the positions of the PA and LNA may be reversed. Figure 4 is a circuit diagram of another example of an EBD 400, which shows this arrangement. The EBD 400 includes some components that are similar to those shown in Figure 2, and similar components are given like reference numerals. However, the EBD 400 omits the PA 214 and LNA 218 shown in Figure 2. Instead, the EBD 400 includes a single-ended PA 402 with an output connected to the node 220 between the second at least part of a transformer winding 206 and the fourth at least part of a transformer winding 212.

[0036] Thus, in some examples, an EBD 400 may comprise a first transformer 202 comprising a first at least part of a transformer winding 204 and a second at least part of a transformer winding 206, and a second transformer 208 comprising a third at least part of a transformer winding 210 and a fourth at least part of a transformer winding 212. The first at least part of a transformer winding 204 is connected in series with the third at least part of a transformer winding 210. The EBD 400 also includes a first amplifier 402 having an output connected to a node 220 between the second at least part of a transformer winding 206 and the fourth at least part of a transformer winding 212, and a second amplifier 404 having an input connected to the first at least part of a transformer winding 204 and / or the third at least part of a transformer winding 210. The second at least part of a transformer winding 206 is connected in series with the fourth at least part of a transformer winding 212 between a first antenna node 222 and a second antenna node 224, wherein the first antenna node 222 is for connection to a first antenna and the second antenna node 224 is for connection to a second antenna.

[0037] In the example shown in Figure 4, the second amplifier (LNA) 404 is a balanced input amplifier, and hence the first at least part of a transformer winding 204 is connected in series with the third at least part of a transformer winding 210 between the balanced inputs of the LNA 404, and the node 216 between the first at least part of a transformer winding 204 and the third at least part of a transformer winding 210 is connected to a reference voltage or ground.

[0038] The two antennas of the EBDs described herein may have the same or different polarizations. Where the polarizations are different, the polarizations may or may not be orthogonal. For example, the antennas may be two vertically polarized antennas, two horizontally polarized antennas, or one vertically and one horizontally polarized antenna.

[0039] In operation, in some examples, referring to the EBD 200 of Figure 2 as an example (with connected antennas), transmission using a signal provided to the PA 214 occurs with half of the transmitted signal +Tx / 2 transmitted from the first antenna 226 and half of the transmitted signal -Tx / 2 from the second antenna 228. The opposite signs indicate differential mode transmission. Reception, on the other hand, occurs with half of a received signal +Rx / 2 received at the first antenna 226 and half of the received signal +Rx / 2 received at the second antenna, assuming that the same amount of received signal is received at both antennas (which may not be the case for example where antennas are located on opposite sides of a device or have different radiation patterns, for example). The same sign indicates a common mode reception. The EBD 400 of Figure 4 operates in a similar manner, where transmission using a signal provided to the PA 402 occurs with half of the transmitted signal +Tx / 2 transmitted from the first antenna 226 and half of the transmitted signal Tx / 2 from the second antenna 228, and half of a received signal +Rx / 2 received at the first antenna 226 and half of the received signal -Rx / 2 received at the second antenna, with the same assumptions.

[0040] The LNA 218 in some examples of the EBD 200 of Figure 2 may be designed to provide an input impedance that matches the two antennas 226 and 228, which appear to the LNA input to be parallel connected, each in series with some inductance from a transformer winding (i.e. at least part of a winding 206 and at least part of a winding 212). The LNA 218 may thus in some examples present a real part impedance of about half of the antenna impedance, and some capacitive imaginary part. The power of the incoming common mode signal will then be absorbed by the LNA input with low reflections or other losses. The 3dB losses otherwise present in known EBDs will hence not occur for common-mode signals in embodiments of this disclosure. If a signal is received by just one of the antennas, however, as would be the case for example if it is in the main lobe direction of that antenna but in a null direction of the other, this can be regarded for example as a combination of a common mode and a differential mode excitation, with half the signal energy in each mode. The differential mode will not produce any input to the LNA, and will hence be rejected, resulting in a 3dB loss. This means that the sensitivity is degraded by 3dB compared to using a single antenna and a matched LNA. However, for a receiver covering the same beam pattern, an antenna with 3dB less gain would be needed to cover the same angular range as the two antennas of the EBDs described herein. The net sensitivity would then be the same, and no receive performance is lost, as embodiments of this disclosure may use antennas with 3dB more gain.

[0041] For the LNA 404 in Figure 4, an LNA with a matched impedance may be used in some examples. For example, each input of the LNA 404 may have an input impedance equal to the impedance of the antenna 226 and / or 228, i.e. the differential input impedance may be two times the antenna impedance. This may be for transformers not transforming the impedance for example. The transformers 202 and 208 may in some examples be designed with a different number of turns in the primary and secondary windings (i.e. in windings 206 and 204, and in windings 212 and 210), and have a different coupling factor, so they transform the impedance between their primary and secondary windings. Then, the differential LNA input impedance may be two times the transformed antenna impedance, for example.

[0042] The transmitted signal from the PA will, if the EBD circuit is perfectly matched, have zero voltage at the input of the LNA 218. If the PA has good differential signal balance, if the two transformers 202 and 208 are well matched, and if the two antennas 226 and 228 and their feeding network are well matched, there will be very low Tx signal leakage to the LNA input. Apart from losses in the transformers 202 and 208, all signal power delivered by the PA 214 will thus be transmitted by the two antennas 226 and 228. The 3dB transmission losses associated with losses in the matching resistor 118 of Figure 1 will hence not occur for embodiments of this disclosure.

[0043] Coupling of signals between the antennas is reciprocal, and if the two antennas are matched this can be modelled for example by an impedance Z connecting the two antenna ports (e.g. the nodes 222 and 224 shown in Figure 2). This impedance will not affect the symmetry of the EBD, and hence the coupling between the two antennas will not degrade the Tx-Rx isolation. In some examples, the EBD according to examples of this disclosure can include additional components to transmit or receive signals on other polarizations. For example, the EBD may effectively include a second EBD for different polarizations to a first EBD.

[0044] Figure 5 is a circuit diagram of another example of an EBD 500 according to embodiments of this disclosure. The EBD 500 includes a first EBD, generally indicated as 502, and a second EBD, generally indicated as 504. The first EBD 502 and second EBD 504 in this example each comprise the EBD 200 shown in Figure 2, though in other examples each EBD may be any EBD according to this disclosure, such as the EBD 400 shown in Figure 4, one of each EBD 200 and 400, or any variants thereof.

[0045] The first EBD 502 is connected to two antennas 506 and 508, and the second EBD 504 is connected to two antennas 510 and 512. Any suitable variation of polarizations and / or radiation patterns of the antennas is envisaged. For example, the antennas 506 and 508 may have the same or different (e.g. orthogonal) polarizations, and the antennas 510 and 512 may have the same or different (e.g. orthogonal) polarizations. In particular examples, antennas 506 and 508 have the same polarization that is orthogonal to the polarization of antennas 510 and 512, antennas 506 and 510 have the same polarization that is orthogonal to the polarization of antennas 508 and 512, or antennas 506 and 512 have the same polarization that is orthogonal to the polarization of antennas 508 and 510.

[0046] Thus, in some examples, an EBD according to embodiments of this disclosure (e.g. the EBD 200 shown in Figure 2 or the EBD 400 shown in Figure 4) may further comprise a third transformer comprising a seventh at least part of a transformer winding and an eighth at least part of a transformer winding and a fourth transformer comprising a ninth at least part of a transformer winding and a tenth at least part of a transformer winding, wherein the seventh at least part of a transformer winding is connected in series with the ninth at least part of a transformer winding. The EBD may also further comprise a third amplifier having an output connected to the seventh at least part of a transformer winding and / or the ninth at least part of a transformer winding, and a fourth amplifier having an input connected to a node between the eighth at least part of a transformer winding and the tenth at least part of a transformer winding. The eighth at least part of a transformer winding may be connected in series with the tenth at least part of a transformer winding between a third antenna node and a fourth antenna node, wherein the third antenna node is for connection to a third antenna and the fourth antenna node is for connection to a fourth antenna. The third amplifier may in some examples be a balanced output amplifier, and wherein the seventh at least part of a transformer winding is connected in series with the ninth at least part of a transformer winding between a first output of the third amplifier and a second output of the third amplifier.

[0047] Alternatively, in some examples, an EBD according to embodiments of this disclosure (e.g. the EBD 200 shown in Figure 2 or the EBD 400 shown in Figure 4) may further comprise a third transformer comprising a seventh at least part of a transformer winding and an eighth at least part of a transformer winding, and a fourth transformer comprising a ninth at least part of a transformer winding and a tenth at least part of a transformer winding, wherein the seventh at least part of a transformer winding is connected in series with the ninth at least part of a transformer winding. The EBD may also further comprise a third amplifier having an output connected to a node between the eighth at least part of a transformer winding and the tenth at least part of a transformer winding and a fourth amplifier having an input connected to the seventh at least part of a transformer winding and / or the ninth at least part of a transformer winding. The eighth at least part of a transformer winding may be connected in series with the tenth at least part of a transformer winding between a third antenna node and a fourth antenna node, wherein the third antenna node is for connection to a third antenna and the fourth antenna node is for connection to a fourth antenna. The fourth amplifier may in some examples be a balanced input amplifier, and wherein the seventh at least part of a transformer winding is connected in series with the ninth at least part of a transformer winding between a first input of the fourth amplifier and a second input of the fourth amplifier.

[0048] In either of these examples, the EBD may also include the third antenna connected to the third antenna node, and the fourth antenna connected to the fourth antenna node. The coverage pattern of the third antenna is different to a coverage pattern of the fourth antenna, e.g. the coverage pattern of the third antenna partially overlaps with the coverage pattern of the fourth antenna, or does not overlap with the coverage pattern of the fourth antenna. In some examples, the third antenna and the fourth antenna are mounted on different surfaces of a device, or on surfaces on opposite sides of the device. The third antenna and the fourth antenna have a matched impedance.

[0049] The third transformer and the fourth transformer may in some examples be portions of a second single transformer. For example, the second single transformer may comprise a eleventh transformer winding comprising the seventh at least part of a transformer winding and the ninth at least part of a transformer winding, and may also comprise a twelfth transformer winding comprising the eighth at least part of a transformer winding and the tenth at least part of a transformer winding. The node between the eighth at least part of a transformer winding and the tenth at least part of a transformer winding may be a centre tap of the twelfth transformer winding.

[0050] In examples of this disclosure, the input of the first amplifier (e.g. PA) may be connected to a transmitter chain or may be a part of a transmitter chain. Similarly, the output of the second amplifier (LNA) may be connected to a receiver chain or may be part of a receiver chain.

[0051] Any of the embodiments of this disclosure may have one or more of the following advantages:

[0052] • Avoids 3dB fundamental insertion losses;

[0053] • Has a similar radiation pattern in Rx and Tx;

[0054] • Straightforward to use isolated antennas in different directions by using antennas on different or opposite sides of a device;

[0055] • Tx-Rx isolation is limited by EBD suppression, which is typically much larger (10- 100x) than isolation between polarizations of close antennas; and / or

[0056] • Symmetry in antenna design and feeding may lead to intrinsic matching between antenna port impedances, and hence no need for tuning of load impedances;

[0057] To provide some understanding about the level of isolation that may be suitable for some examples of this disclosure, assume the two antennas of an EBD radiate in opposite directions, such as being on opposite sides of a device as shown in Figure 3 for example. If each antenna then radiates -20dB in the back-lobe direction, if the signals add constructively or destructively, the difference in the combined transmitted signal will be + / - 0.8dB. Some other back-lobe levels and their constructive and destructive combinations are shown in the table below:

[0058] About -20dB of back-lobe level, or isolation between the antenna patterns, is sufficient to provide a small difference in the combined radiation pattern, since then the difference between constructive and destructive combination is + / -0.8dB = 1 ,6dB. If the Tx signal combines constructively, the Rx signal will combine destructively, and vice versa. It is therefore desirable to have a small difference between the two modes of combination. As can be seen in the table above, 6dB of isolation between the antenna patterns would not be sufficient, as the difference between the modes can then reach almost 10dB.

[0059] It should be noted that the above-mentioned examples illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative examples without departing from the scope of the appended statements. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the statements below. Where the terms, “first”, “second” etc. are used they are to be understood merely as labels for the convenient identification of a particular feature. In particular, they are not to be interpreted as describing the first or the second feature of a plurality of such features (i.e. , the first or second of such features to occur in time or space) unless explicitly stated otherwise. Steps in the methods disclosed herein may be carried out in any order unless expressly otherwise stated. Any reference signs in the statements shall not be construed so as to limit their scope.

Claims

Claims1. An electrical balance duplexer, EBD (200, 500), comprising: a first transformer (202) comprising a first at least part of a transformer winding (204) and a second at least part of a transformer winding (206); a second transformer (208) comprising a third at least part of a transformer winding (210) and a fourth at least part of a transformer winding (212), wherein the first at least part of a transformer winding is connected in series with the third at least part of a transformer winding; a first amplifier (214) having an output connected to the first at least part of a transformer winding and / or the third at least part of a transformer winding; and a second amplifier (218) having an input connected to a node (220) between the second at least part of a transformer winding and the fourth at least part of a transformer winding; wherein the second at least part of a transformer winding is connected in series with the fourth at least part of a transformer winding between a first antenna node (222) and a second antenna node (224), wherein the first antenna node is for connection to a first antenna (226, 302, 506) and the second antenna node is for connection to a second antenna (228, 304, 508).

2. An electrical balance duplexer, EBD (400, 500), comprising: a first transformer (202) comprising a first at least part of a transformer winding (204) and a second at least part of a transformer winding (206); a second transformer (208) comprising a third at least part of a transformer winding (210) and a fourth at least part of a transformer winding (212), wherein the first at least part of a transformer winding is connected in series with the third at least part of a transformer winding; a first amplifier (402) having an output connected to a node (220) between the second at least part of a transformer winding and the fourth at least part of a transformer winding; and a second amplifier (404) having an input connected to the first at least part of a transformer winding and / or the third at least part of a transformer winding; wherein the second at least part of a transformer winding is connected in series with the fourth at least part of a transformer winding between a first antenna node (222) and a second antenna node (224), wherein the first antenna node is for connection to a firstantenna (226, 302, 506) and the second antenna node is for connection to a second antenna (228, 304, 508).

3. The EBD of claim 1 or 2, further comprising: the first antenna (226, 302, 506) connected to the first antenna node (222); and the second antenna (228, 304, 508) connected to the second antenna node (224).

4. The EBD of claim 3, wherein a coverage pattern of the first antenna (226, 302, 506) is different to a coverage pattern of the second antenna (228, 304, 508).

5. The EBD of claim 4, wherein the coverage pattern of the first antenna (226, 302, 506) partially overlaps with the coverage pattern of the second antenna (228, 304, 508), or does not overlap with the coverage pattern of the second antenna.

6. The EBD of any of claims 3 to 5, wherein the first antenna (226, 302, 506) and the second antenna (228, 304, 508) are mounted on different surfaces of a device (300), or on surfaces on opposite sides of the device.

7. The EBD of any of claims 3 to 6, wherein the first antenna (226, 302, 506) and the second antenna (228, 304, 508) have a matched impedance.

8. The EBD of any of claims 1 to 7, wherein the first transformer (202) and the second transformer (208) are portions of a first single transformer.

9. The EBD of claim 8, wherein the first single transformer comprises: a fifth transformer winding comprising the first at least part of a transformer winding (204) and the third at least part of a transformer winding (210); and a sixth transformer winding comprising the second at least part of a transformer winding (206) and the fourth at least part of a transformer winding (212).

10. The EBD of claim 9, wherein the node (220) between the second at least part of a transformer winding (206) and the fourth at least part of a transformer winding (212) comprises a centre tap of the sixth transformer winding.

11. The EBD of any of claims 1 to 10 when dependent on claim 1 , wherein the first amplifier (214) is a balanced output amplifier, and wherein the first at least part of a transformer winding (204) is connected in series with the third at least part of a transformerwinding (210) between a first output of the first amplifier and a second output of the first amplifier.

12. The EBD of any of claims 2 to 11 when dependent on claim 2, wherein the second amplifier (404) is a balanced input amplifier, and wherein the first at least part of a transformer winding (204) is connected in series with the third at least part of a transformer winding (210) between a first input of the second amplifier and a second input of the second amplifier.

13. The EBD of any of claims 1 to 12, further comprising: a third transformer comprising a seventh at least part of a transformer winding and an eighth at least part of a transformer winding; a fourth transformer comprising a ninth at least part of a transformer winding and a tenth at least part of a transformer winding, wherein the seventh at least part of a transformer winding is connected in series with the ninth at least part of a transformer winding; a third amplifier having an output connected to the seventh at least part of a transformer winding and / or the ninth at least part of a transformer winding; a fourth amplifier having an input connected to a node between the eighth at least part of a transformer winding and the tenth at least part of a transformer winding; wherein the eighth at least part of a transformer winding is connected in series with the tenth at least part of a transformer winding between a third antenna node and a fourth antenna node, wherein the third antenna node is for connection to a third antenna (510) and the fourth antenna node is for connection to a fourth antenna (512).

14. The EBD of any of claims 1 to 12, further comprising: a third transformer comprising a seventh at least part of a transformer winding and an eighth at least part of a transformer winding; a fourth transformer comprising a ninth at least part of a transformer winding and a tenth at least part of a transformer winding, wherein the seventh at least part of a transformer winding is connected in series with the ninth at least part of a transformer winding; a third amplifier having an output connected to a node between the eighth at least part of a transformer winding and the tenth at least part of a transformer winding; a fourth amplifier having an input connected to the seventh at least part of a transformer winding and / or the ninth at least part of a transformer winding;wherein the eighth at least part of a transformer winding is connected in series with the tenth at least part of a transformer winding between a third antenna node and a fourth antenna node, wherein the third antenna node is for connection to a third antenna (510) and the fourth antenna node is for connection to a fourth antenna (512).

15. The EBD of claim 13 or 14, wherein: the first antenna (226, 302, 506) has the same polarization as the third antenna (510), and the second antenna (228, 304, 508) has the same polarization as the fourth antenna (512) and a different polarization to the first antenna and the third antenna; or the first antenna has the same polarization as the second antenna, and the third antenna has the same polarization as the fourth antenna and a different polarization to the first antenna and the second antenna.

16. The EBD of any of claims 12 to 15, further comprising: the third antenna (510) connected to the third antenna node; and the fourth antenna (512) connected to the fourth antenna node.

17. The EBD of claim 16, wherein a coverage pattern of the third antenna (510) is different to a coverage pattern of the fourth antenna (512).

18. The EBD of claim 17, wherein the coverage pattern of the third antenna (510) partially overlaps with the coverage pattern of the fourth antenna (512), or does not overlap with the coverage pattern of the fourth antenna.

19. The EBD of any of claims 16 to 18, wherein the third antenna (510) and the fourth antenna (512) are mounted on different surfaces of a device, or on surfaces on opposite sides of the device.

20. The EBD of any of claims 16 to 19, wherein the third antenna (510) and the fourth antenna (512) have a matched impedance.

21. The EBD of any of claims 13 to 20, wherein the third transformer and the fourth transformer are portions of a second single transformer.

22. The EBD of claim 21, wherein the second single transformer comprises: a eleventh transformer winding comprising the seventh at least part of a transformer winding and the ninth at least part of a transformer winding; anda twelfth transformer winding comprising the eighth at least part of a transformer winding and the tenth at least part of a transformer winding.

23. The EBD of claim 22, wherein the node between the eighth at least part of a transformer winding and the tenth at least part of a transformer winding comprises a centre tap of the twelfth transformer winding.

24. The EBD of any of claims 13 to 23 when dependent on claim 13, wherein the third amplifier is a balanced output amplifier, and wherein the seventh at least part of a transformer winding is connected in series with the ninth at least part of a transformer winding between a first output of the third amplifier and a second output of the third amplifier.

25. The EBD of any of claims 14 to 23 when dependent on claim 14, wherein the fourth amplifier is a balanced input amplifier, and wherein the seventh at least part of a transformer winding is connected in series with the ninth at least part of a transformer winding between a first input of the fourth amplifier and a second input of the fourth amplifier.

26. A device (300) comprising the electrical balance duplexer, EBD (200, 400, 500) of any of claims 1 to 25.

27. The device of claim 26, wherein the device comprises a transceiver or a wireless communication device.

28. The device of claim 27, further comprising: the first antenna (226, 302, 506) connected to the first antenna node (222); and the second antenna (228, 304, 508) connected to the second antenna node (224).

29. The device of claim 28, wherein a coverage pattern of the first antenna (226, 302, 506) is different to a coverage pattern of the second antenna (228, 304, 508).

30. The device of claim 29, wherein the coverage pattern of the first antenna (226, 302, 506) partially overlaps with the coverage pattern of the second antenna (228, 304, 508), or does not overlap with the coverage pattern of the second antenna.31 . The device of any of claims 28 to 30, wherein the first antenna (226, 302, 506) and the second antenna (228, 304, 508) are mounted on different surfaces of the device, or on surfaces on opposite sides of the device.

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